This invention is concerned with improving solar heating panels. The invention is particularly directed to an improved coating for solar heating panels. The coating has high absorptivity for visible solar radiation and low emissivity for infrared radiation.
Solar collectors are devices that collect energy from the sun for conversion to heat and electrical power. These devices utilize flat composite panels to collect the energy.
Selective coating of the heating panels has been suggested to increase the energy absorbing properties. By way of example, a solar heating panel may be coated with black paint which is inexpensive and absorbs a great amount of solar energy. However, it has been found that paint flakes, chips, and is not very durable. Black paint also enables much of the absorbed energy to be lost by emittance.
Black nickel has also been used as a coating for solar heating panels. Black nickel is a good heat conductor, but coatings of this material are vulnerable to moisture.
Various attempts have been made to improve the black nickel coatings. For example, a substrate is first coated with bright nickel and then overlaid with a layer of black nickel. However, this bright-black nickel selective coating has been difficult to control in the deposition of black nickel coating in order to achieve the desired optimum properties and coating thickness. As the black nickel is being deposited, the substrate cannot be removed from the plating bath without the requirements for stripping the black nickel and restarting the deposition process again. Also, the black nickel, as deposited, is still subject to corrosion from the atmosphere and other sources.
Other thin exposed light-absorptive and heat transparent surface coatings are disclosed in U.S. Pat. No. 2,917,817 to Tabor. These coatings are in heat conductive relation to a bright metal base. Solar heating panels utilizing these coatings have been expensive and difficult to produce.